The present invention relates generally to a decoder for spectrum diffusion signals, which is specially adapted for satellite communications utilizing spectrum diffusion signals.
Spectrum diffusion communications systems (hereafter called as "SS communications systems") are know to be advantageous in that they can use pseudo-random-noise signals (hereafter referred to as "PRN signals") which allow sufficiently precise frequency channel selection and thus satisfactorily avoid interference among communication channels. Therefore, information security can be guaranteed by use of such SS communications systems. In addition, such SS communications systems have the advantage that PRN signals have a relative high band width for modulating data signals.
In such SS communications systems, received satellite signals must be demodulated in the receiving station. In order to demodulate the satellite signal, processing by back-diffusion has to be performed utilizing a Gold code specific to the station to keep the specific communications channel secure.
For such back-diffusion process, it has been conventionally believed that the phase of the Gold code must be synchronized with the phase of the received PRN signal by the decoder itself when checking the codes for a match. This synchronization will be referred to hereafter as "PN synchronization". Therefore, conventional decoders for spectrum diffusion signals have required means for performing PN synchronization, such as sliding correlating loops or matched filters or the like. Such means for performing PN synchronization prevents simplification of the decoder circuitry.